1. Field of the Invention
The present invention relates to a pointing device which is used to move a pointer or cursor on a display of an electronic device such as a computer, word processor, or the like to an arbitrary position on the display, and a keyboard mounting thereon the pointing device, and an electronic device provided with the keyboard.
2. Description of Related Art
In an electronic device provided with a display, such as a computer, word processor, or the like, generally, there is connected or mounted a pointing device whereby a pointer or cursor can be moved on a display to an arbitrary position without the need of key operations. One type of such the pointing device is arranged so as to detect the amount of strain which occurs when an operator places his finger tip on a stick member vertically provided in a keyboard, thereby applying a force on the stick member backward and frontward, or rightward and leftward, and then to move a pointer or cursor based on the detected strain amount.
In Japanese patent unexamined publication No. 8-87375, for example, as shown in FIG. 13, a pointing device is provided with a stick member 52 disposed at a center of a strain detecting substrate 51, strain sensors 53 arranged at four positions (only two of them are illustrated in FIG. 13), namely, a front, back, right, and left positions with respect to the stick member 52, and a base substrate 54 on which the strain detecting substrate 51 is attached with an internal gap. The strain sensors 53 detect the amount of strain (deformation) of the strain detecting substrate 51 generated at the gap with respect to the base substrate 54 when a force is applied on the stick member 52. This strain amount is subjected to a signal-processing in a processing circuit provided in the base substrate 54 side.
However, the above configuration that the base substrate 54 is attached to the strain detecting substrate 51 needs individual formation of print patterns on the substrates 51 and 54. Therefore, a patterning step should be repeated twice, resulting in deterioration in the productivity. The strain detecting substrate 51 also has to be attached by soldering to the base substrate 54 while a worker confirms positioning of the substrate 51 thereto. Accordingly, yields are likely to decrease due to soldering failures or the like during the attachment work. Furthermore, since the strain detecting substrate 51 is stacked on the base substrate 54, such a complex structure is prone to cause expensive assembling costs and malfunctions.
Furthermore, there has also been proposed a pointing device constructed, as shown in FIG. 14, such that a stick member 152 is disposed at a center of a strain detecting substrate 151, four strain sensors 153 are arranged at a front, back, right, and left positions with respect to the stick member 152, and notches 153a are formed with a laser beam irradiated to scan the strain sensor 153 from each end by a predetermined distance, thereby removing electric resistance (a trimming process), in order to prevent the inconsistency in an offset voltage outputted due to the sensors 153. The strain detecting substrate 151 is then attached to a base substrate 154 with a gap between the substrates 151 and 154. When a force is applied on the stick member 152, the amount of strain (deformation) of the substrate 151 at the gap with respect to the base substrate 154 is detected based on an electric current allowed to pass through the strain sensors 153, and the detected current values are signal-processed in a processing circuit provided in the base substrate 154 side.
However, the above structure has the following disadvantages. When the laser beam is irradiated to scan the strain sensor 153 from each end in the trimming process, the laser beam tends to concentrate at a point in a scanning stop position (an endpoint of the notch 153a), as shown in FIG. 15, which gives a large amount of heat of the laser beam to the endpoint of the notch 153a. The large heat amount would cause an excessive rise in the temperature of the electric resistance of a peripheral region 153b of the endpoint. This excessive temperature rise may bring the electric resistance into an unstable state as a resistance due to thermal stress, that is, into a state where a resistance value is liable to change with reference to temperatures, current values, and physical noises. As a result, the current i fluctuates by an amount corresponding to the change of the resistance value in the peripheral region 153b, operating as a noise element of detected current values, which may cause malfunctions in the electronic device mounting the pointing device.